Britons flocked to the polls in a general election on Thursday that could end 13 years of Labour rule and thrust the small Liberal Democratic Party into a decisive role.
Prime Minister Gordon Brown, whose political survival is seen as being at stake in this election, cast his vote in his constituency in his native Scotland, flanked by his wife, Sarah.
"Good to see you all," he told election workers, managing a smile despite persistent drizzle and grey skies.
Earlier this week, Brown's Labour Party had slipped to third position, prompting comment about a feared "meltdown" of the party which has ruled Britain since 1997.
Cameron, accompanied by his pregnant wife, Samantha, voted in Oxfordshire while Nick Clegg, the Liberal leader, attended a polling station in Sheffield, northern Britain.
His wife, Spanish lawyer Miriam Gonzales Durantez, who was with him, could not vote as she does not have British citizenship.
Polling day was overshadowed by the crash of a light aircraft carrying Nigel Farage, a candidate for the anti-European United Kingdom Independence Party (UKIP).
The 46-year-old former leader of UKIP, who is also a Member of the European Parliament (MEP), escaped the crash of the two-seater aircraft with light head injuries, a party spokesman said.
The accident was believed to have been caused by an election banner the plane was towing, urging a UKIP vote, becoming entangled with the aircraft.
A string of six opinion polls for national newspapers were unanimous on Thursday in placing the opposition Conservatives, led by David Cameron, in the lead by a comfortable margin.
But they were also united in suggesting that Cameron will not achieve the overall majority he needs to become prime minister at the head of a majority conservative administration, requiring him to call on the support of the Liberal Democrats.
The figures show that the Tories could win between 35 and 37 per cent of the popular share of the vote, with the ruling Labour Party between 27 and 29 per cent and between 26 and 28 per cent for the Liberal Democrats.
This could result in a hung parliament and give the Liberals the balance of power and thrust them into the role of kingmaker.
The 43-year-old Liberal leader was widely seen as the "star" of the election campaign following his refreshing and convincing performance during televised leaders' debates - a novelty in Britain.
An opinion poll published Thursday showed that almost a fifth of voters said they switched their party allegiance as a result of the three debates.
However, under the vagaries of Britain's first-past-the-post electoral system, opinion poll popularity ratings say little about the actual number of seats won in the 649 constituencies across the country.
Of the 45 million Britons entitled to vote, about a third were said to be still undecided, surveys showed. The number of constituencies fell by one from 650 after the death of a candidate, it was announced on Thursday.
After a lively four-week campaign, turnout is expected to be up, possibly at around 70 per cent, a figure not seen since the landmark 1997 election won by former prime minister Tony Blair.
Polling stations opened at 7 am (0600 GMT) and are to close at 10 pm Official results are not expected until the early hours of Friday.